The present invention relates generally to systems and methods for data communications, and more particularly, to systems and methods for relaying data in a multihop relay network architecture.
The demand for quality of service (“QoS”) in wireless networking systems has been addressed by the IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard. The IEEE 802.16 standard adopts a polling-based media access control (“MAC”), which is more deterministic than the contention-based MAC used by the 802.11 standard. The 802.16's MAC layer enables classification of QoS and non-QoS dependant application flows and maps them to connections with distinct scheduling services, enabling both guaranteed handling and traffic enforcement. In the point-to-multipoint (“PMP”) architecture specified in the IEEE 802.16 standard, data are directly transmitted between a base station (BS) and a mobile station (MS). However, to improve throughput and amplify the service range of a BS, the Mobile Multihop Relay (“MMR”) Task Group has revised the IEEE 802.16 standard such that an MS is able to communicate in both uplink and downlink connections with a BS through a relay station (“RS”). Imagine that a BS sends data to or receives data from plural MS's through plural RS's, which is sure to happen in the MMR network architecture. An issue may arise regarding how to transmit data in a simple and efficient manner. Another issue may arise as to how a BS maps data with one MS of a plurality of MS's.
FIG. 1 is a schematic diagram a system 10 using a conventional tunneling approach in an MMR network. Referring to FIG. 1, the system 10 includes a base station labeled BS, a first relay station labeled RS1, a second relay station labeled RS2 and a mobile station labeled MS. The BS assigns connection identifiers (“CID”s) CID1, CID3 and CID5 to the RS1, RS2 and MS, respectively, and allocates time intervals t1, t2 and t3 for the connections CID1, CID3 and CID5, respectively. In a downlink transmission, a payload is to be transmitted from the BS to the MS through the RS1 and RS2. In operation, during the time interval t1 corresponding to CID1, the BS sends a first protocol data unit (“PDU”) including the payload prefixed with CID1, CID3 and CID5 as headers for control the transfer of the payload. Meanwhile, RS1 receives the first PDU sent from the BS. RS1 then prepares a second PDU by removing the header CID1 from the first PDU. During the time interval t2 corresponding to CID3, RS1 sends the second PDU including the payload prefixed with CID3 and CID5 as headers to RS2. Similarly, RS2 then prepares a third PDU by removing the header CID3 from the second PDU sent from RS1. During the time t3 corresponding to CID5, RS2 sends the third PDU including the payload prefixed with CID5 as header to the MS. The above-described tunneling approach may be simple in operation but requires more headers as the transmission path is longer, which adversely affects the throughput. Moreover, adding the headers at the BS before transmission and removing the headers at the relay stations during transmission may further deteriorate the throughput. Consequently, the tunneling approach may not be a desired method for data relay in the MMR network architecture. It is desirable to have a system and a method that is able to transmit data in a simple and efficient manner, and ensure correct transmission between a BS and an MS through at least one RS.